The present invention relates to a display device, and more particularly to a display device which forms thin film transistors on a substrate.
As such a display device, there has been known a display device which is configured such that thin film transistors for selecting pixels are formed in respective pixels with in a display region on a substrate surface of the display device and, at the same time, a peripheral circuit for driving the respective pixels is formed on a periphery of the display region, and the peripheral circuit includes a plurality of thin film transistors.
Here, in manufacturing such a display device, for enhancing the manufacturing efficiency of the display device, usually, the thin film transistor for selecting the pixel and the thin film transistor for the peripheral circuit are formed simultaneously with each other.
Further, there has been known a technique in which as a thin film transistor for selecting a pixel, a semiconductor layer is made of amorphous silicon (a-Si), while as a thin film transistor of the peripheral circuit, a semiconductor layer is made of poly-crystalline silicon which is produced by crystallizing amorphous silicon using a pseudo single crystal technique, for example. This technique is adopted because when the semiconductor layer is made of polycrystalline silicon, it is possible to obtain a thin film transistor having excellent mobility.
In this case, there has been known that, by using a silicon nitride film as a gate insulation film in a thin film transistor which forms the semiconductor layer using amorphous silicon, and by using a silicon oxide film as a gate insulation film in a thin film transistor which forms a semiconductor layer using polycrystalline silicon, it is possible to enhance characteristics of the respective thin film transistors.
The display device having such constitution is disclosed in JP-A-5-107560 (patent document 1) with a manufacturing method of the display device.